The commission rates are well calculated. From what i remember we started with 30% so you should be happy with 50% or more. The math is simple – low volumes of sales -> 50% = x ammount of cash. X will be alwats lower than an author that has higher volumes of sales -> 70%, so why from a business point of view would you reduce the income where it’s already low? Put more work into your items, don’t bother with coping, be original and you’ll get to 70%.